Conventionally, as a protective case for protecting a control board from outside dust and dirt and rain drops has been generally used a case of the type in which: support rails are provided on the left and right peripheral walls of a housing for housing the control board; the control board is inserted into the housing along the support rails; and the housing is fixed with a cover (for example, see Patent Document 1).
Further, there has been considered a structure in which, in place of the support rails, a plurality of protruding parts (ribs) are formed on the peripheral wall of a housing alternately in a depth direction of the housing at a spacing corresponding to a designed thickness of the upper and lower surfaces of the control board, whereby even if the control board is formed in a thickness a little larger than a specified spacing of the protruding portion, the control board is bent and inserted along the ribs, thereby being surely fixed in the housing (for example, see Patent Document 2).